1. Field of the Invention
This invention relates to an intermittent transmission mechanism for converting a continuous rotational displacement into an intermittent rotational displacement for transmission.
2. Description of the Prior Art
As an example of intermittent transmission mechanism of this type, a Geneva drive mechanism has been proposed which is disclosed in Japanese Utility Model Publication Kokai H6-40507. As shown in FIG. 8 of this reference, this apparatus includes a driven rotor 03 having engageable elements in the form of a plurality of slots 02 opening radially outwardly. The plurality of slots 02 and a plurality of recesses 01 are arranged alternately at predetermined intervals peripherally of the driven rotor 03. Further, a driving rotor 06 has an engaging element in the form of an engaging roller 04 for sequentially engaging the plurality of slots 02 of driven rotor 03 to rotate the driven rotor 03 intermittently by a predetermined angle. The driven rotor 03 has also a plurality of freely rotatable rotating rollers 05 attached thereto for contacting arcuate surfaces 01a of the recesses 01 of driven rotor 03 when the driven rotor 03 stops with the engaging roller 04 disengaged from the slots 02.
In the Geneva drive mechanism having the above construction, the number of slots 02 formed in the driven rotor 03 corresponds to the number of intermittent rotations (hereinafter called dividing number) per complete rotation of driven rotor 03. When the driving rotor 06 rotates to engage the engaging roller 04 in one of the slots 02 of driven rotor 03, the driven rotor 03 is rotated until the engaging roller 04 becomes disengaged from the slot 02. The rotation of driven rotor 03 is stopped until the engaging roller 04 engages a next slot 02 disposed upstream in the direction of rotation of the slot 02 from which the engaging roller 04 is disengaged
When the rotation of driven rotor 03 is stopped, the rotating rollers 05 of driving rotor 06 rotate in contact with the arcuate surface 01a of non-drive recess 01 of driven rotor 03, and move with the driving rotor 06 along the arcuate surface 01a.
With the conventional intermittent transmission mechanism in the form of a Geneva drive mechanism, when the driven rotor 03 is stopped, an excessive workload on an output line of driven rotor 03 may be transmitted back to the driven rotor 03 as a strong torque. This strong torque reaction concentrates on support axes 05a of the rotating rollers 05 of driving rotor 06 contacting the arcuate surface 01a of non-drive recess 01 of driven rotor 03, or concentrates on a proximal portion of driven rotor 03 lying between the slots 02 adjacent each other in the direction of rotation and having a minimum width W in the direction of rotation. The support axes 05a or the proximal portion with the minimum width could be broken.
When the driven rotor 03 is rotated intermittently and the excessive workload on the output line of driven rotor 03 acts as a strong reaction on the driven rotor 03, the reaction concentrates on a support axis 04a of the engaging roller 04 of driving rotor 06 engaged in a slot 02 of driven rotor 03. Thus, the support axis 04a could be broken.
Therefore, in case a great workload occurs on the output line of driven rotor 03, the support axis 04a of engaging roller 04 may be formed with an increased diameter to increase the maximum permissible stress of support axis 04a. In this case, however, where only the diameter of support axis 04a is simply enlarged, the diameter of engaging roller 04 also is inevitably enlarged. As a result, the slots 02 have an enlarged opening width in the direction of rotation, and the minimum width W of the proximal portions becomes correspondingly small. Actually, therefore, it is necessary to enlarge both a maximum radius R of driven rotor 03 and a distance r from a rotational axis of driving rotor 06 to a center axis of engaging roller 04. This has resulted in the enlargement of the intermittent transmission mechanism.
In addition, an increase in the number of slots 02 formed in the driven rotor 03, i.e. the dividing number, reduces an angle of rotation from engagement to disengagement of engaging roller 04 into/from a slot 02 and an engaging depth radially of the direction of rotation. This results in an increase in the maximum radius R of driven rotor 03, thereby enlarging the intermittent transmission mechanism. Conversely, a decrease in the dividing number increases the angle of rotation from engagement to disengagement of engaging roller 04 into/from a slot 02 and the engaging depth radially of the direction of rotation. This reduces the width of the minimum width proximal portions of the driven rotor, which may cause breakage as noted hereinbefore.
This invention has been made having regard to the state of the art noted above, and its object is to provide an intermittent transmission mechanism, with a devised transmission structure of a driving rotor and a driven rotor, for allowing the dividing number to be set as desired while ensuring improved strength to withstand a workload and a compact construction, and for stopping rotation of the driven rotor with increased precision.